There is a commercial demand for antennas that operate in the millimeter wave region, equating to frequencies in the range 30-300 GHz. Such antennas find application in Wireless Personal Area Networks (WPANs) used in the wireless transmission of high definition television data and for high-speed internet access, and also in video on demand and short-distance high data-rate transmission used to replace fixed cabling.
A similar demand also exists for antennas that operate below millimeter wavelengths, down to 1 GHz, for use in Wireless Local Area Networks (WLANs).
Circularly polarised antennas are of interest because they do not need to be aligned/oriented in the way that do linearly polarised antennas to send or receive radio waves. A circular polarised antenna need only be directed towards another circularly (or linearly) polarised antenna.
Known circularly polarised antennas operating at millimeter wave frequencies typically rely upon Low-Temperature Cofired-Ceramic (LTCC) materials, and use arrays of apertures fed by waveguide feed networks, such as that described in Uchimura, H., Shino, N., and Miyazato, K., “Novel circular polarized antenna array substrates for 60 GHz-band,” 2005 IEEE MTT-S International Microwave Symposium Digest, pp. 1875-1878, 12-17 Jun. 2005.
Another example of a circularly polarized antenna is taught by K.-L. Wong, J.-Y. Wu and C.-K. Wu, “A circularly polarized patch-loaded square-slot antenna”, Microwave and Optical Technology Letters, vol 23, no. 6, pp. 363-365, Dec. 20, 1999. Wong et al teaches a patch-loaded square-slot antenna that uses a rectangular patch as the perturbation element for the excitation by a slot of two orthogonal, phase shifted resonant modes of circularly polarized radiation.
It is also of interest to achieve high-gain and wide bandwidth in circularly polarized antennas, which can not be achieved by the two exemplary known antennas referred to immediately above.
U.S. Pat. No. 4,843,400, Tsao et al, issued on Jun. 27, 1989, teaches an array of radiating patch elements mounted on a single waveguide that enables the synthesis of a larger aperture than would be the case for a single antenna element.
A paper by P. S. Hall, “Application of sequential feeding to wide bandwidth, circularly polarised microstrip patch arrays”, IEE Proc., Vol. 136, Pt. H, No. 5, October 1989, pp. 390-398, describes the sequential rotation of the feeding of circularly polarised microstrip patch antennas and arrays coupled with appropriate offset of the feeding phase leads to significant improvements both in bandwidth and purity.